Fluid pressure control device



'mgl? 32.. L A, MAJNE;

FLUID PRESSURE CONTROL DEVICE Filed Aug. 1, 1941 2 Sheets-Sheet 1 INVENTOR. LUDWIG A, MAJNE Rl ATTORNEYS Patentcd Dec. 15, 1942 FLUID PRESSURE min-DEVICE Ludwig A. Maincrl, Grosse Pointe, Mich.,v asdgnor Aircraft to The Warner Corporation, Detroit,

Mich., a corporation of Michigan Application August 1. 1941, Serial N0. 405,086

- schim. The invention relates to fluid pressure control devices and refers more particularly to fluid pressure control devices for hydraulic brakes of airplanes.

The invention has for an object to provide an improved fluid pressure control device of the compound type.

The invention has for another object to so construct the device that the pistons are yieldably advanced during the low pressure stage and positively advanced during the high pressure stage.

The invention has for a further object to so construct thedef/ice that the reservoir is placed in communication with the larger diameter cylinder during thehigh pressure stage to4 reduce the applying 'force which would otherwise be required.

With these and othe'.` objects in view, the invention resides in the novel features of construction and combinations and arrangements of parts as more fully hereinafter set forth.

In the drawings:

Figure 1 is a vertical central section through a fluid pressure control device embodying my invention;

Figures 2 and 3 are similar views showing the parts in different position during the operation of the device; m

Figures 4 and 5 are views similar to Figure l showing other embodiments of my invention;

Figui-eso, '1, 8 and 9 are views similar to a portion of .Figure 5 showing other modifications.

The fluid pressure control device is particularly applicable to a hydraulic brake system of an alrplane, but it is apparent that the device may beV used with other hydraulic brake systems. While the devices as shown do not incorporate the parking features of my Patent No. 2,115,174 lssued April 26, 1938, and Patent No. 2,120,073 issued June '7, 1938, the parking features may be readily incorporated in accordance with the teachings of the patents.

Referring to Figures 1, 2 and 3, the fluid pressure control device occupies a. substantially vertical position and comprises the axially aligned lower or forward cylinder I, upper or rearward cylinder 2, braking fluid reservoir 3 above or beyond the upper cylinder 2, rear or upper end fitting 4, piston rod 5, and mechanism operated by the piston rod for producing fluid pressure. The lower cylinder I is closed at its lower end by the plug 6 and the sealing cup l through both of which the piston rod 5 axially extends. The lower cylinder is provided near its lower 'end with the discharge port l which is adapted to be connected to the` wheel cylinders by the usual tubing (not shown). The upper cylinder 2 is of larger diameter and consequently of greater capacity than the lower cylinder I. The upper end fitting 4 has a dependingannular flange preferably threaded into the upper end of the upper cylinder 2. The fitting is provided with a suitable vent Q placing the reservoir I in communication with the atmosphere and also preferably provided with a suitable bushing Il for engaging a pivot pin of a suitable support.

The piston rod E is constructed to be pivotally connected to a suitable foot pedal for longitudinally moving the piston rod downwardly or forwardly to operate the control device.

The rmechanism operated by the piston rod comprises the lower and upper pistons II and I2, respectively, and also valve mechanism Il. The lower piston II has a body formed of the sleeve Il slidable within the lower cylinder I and thc head I5 at the lower end of the sleeve and slidably engaging the piston rod 5 which extends axially therethrough. The lower piston also has the sealing cup Il preferably formed of rubber abutting the lower side of the head and provided with concentric lips for slidably engaging the wall of the lower cylinder I and also the piston rod 5. The upper piston has a body formed of the sleeve I'I slidable within the upper cylinder 2 and the head Il at the lower end of the sleeve. 'I'he upper piston also has the sealing cup I9 preferably formed of rubber and abutting the lower side of the head and provided with concentric lips, the outer of which slidably engages the wall of the upper cylinder 2 and the inner of which engages l the upper end of the sleeve I4 of the lower piston. The upper piston also comprises the cup 2li having its side wall threadedly engaging the sleeve I1 and its bottom wall abutting the head Il. It will be noted that the cup 2I| forms a part of the bottom of the reservoir 3. For the purpose of facilitating the flow of braking iiuid, which is preferably liquid, from the reservoir into the upper cylinder 2 during the return of the upper piston to its normal or oi position, the sleeve I1 is provided with the external longitudinally extending grooves 2I.

The head I8 of the upper piston has the axial passageway 22 therethrough and the bottom of the cup 20 has the annular series of passageways 23 therethrough registering'with the upper end of the passageway 22 near its periphery. The head I8 is formed with the depending concentric projection 2l having at its lower end the annular flange 25 extending toward its axis, the projection and annular iiange both bounding the passageway 22. The projection 24 is externally threaded for engagement with internal threads on the upper end portion of the sleeve I4 of the lower piston II, the connection being such that both the lower and upper pistons are positively connected to be moved in unison. Also by reason of the passageways 22 and 23 the reservoir is placed in communication with the interior of the sleeve. To place the annular space between the Wall of the upper cylinder 2 and the sleeve I4 in communication with the interior of thev sleeve, the latter is provided with the annular series of transverse holes 26 located slightly below the inner lip of the sealing cup I9 and the upper end of the cup-shaped retainer 21 is provided with the radial grooves 23. The retainer 21 encircles the sleeve I4 below the openings 26 and is supported upon the annular shoulder 29 on the sleeve I4 and the upper end of the retainer abuts the sealing cup I9 between its lips to hold the sealing cup against the head I3 of the upper piston body.

' The piston rod 5 is formed with by-pass means for the lower piston I I to place the lower and Upper Cylinders in communication and this means comprises a passageway formed of the lower andv upper radial bores 30 and 3I, respectively, and the axial bore 32 connecting the lower and upper bores. When the parts are in their normal or off position, the lower radial bores are below the inner lip of the sealing cup I6 and the upper radial bores are above the head I of the lower piston body. The piston rod also has the annular enlargement 33 above the radial bores 3| providing the annular lower i'ace 34 engageable with the central raised face 35 of the head I5 to close the by-pass means for the lower piston and also to move the lower piston downwardly or forwardly, or to advance the same. It will be noted that the annular enlargement formalin effect, a valve for controlling the lower piston by-pass means. The upper end portion of the piston rod 5 is formed with the hollow enlargement 36 to the upper end of which is threadedly secured the cap 31. The portion of the axial bore between the chamber formed in the enlargement 36 and the radial bores 3I is closed by the plug 38 preferably brazed in place. 39 is a valve having the body 40 extending through the axial passageway 22 in the head I8 of the upper piston body. The valve body is provided with the,annular enlargement 4I which is located between the annular flange 25 of the head I8 and the bottom wall of the cup 20, there being clearance to provide for axial movement of the valve relative to the upper piston. 'Ihe lower face of the annular enlargement 4I is adapted to seat upon the annular gasket 42 secured to the upper face of the annular iiange. 25. The valve also has the depending shank 43 which extends through the cap 38 and axially downwardly within the chamber formed within the enlargement 36 at the upper end of the piston rod. The Valve is yieldably connected to the piston rod by means of the coil spring 44 encircling the shank 43 and abutting the cap 38 and the nut 45 threaded upon the lower end of the shank` The spring is calibrated to move the valve with the piston rod until a predetermined pressure of the braking iluid within the lower and upper cylinders I and 2 is created, this pressure being such that all clearance oi the wheel brakes will be taken up before the spring yields. The valve'body 40 is provided with the axial passageway 46 therethrough having its lower end portion reduced and adapted t be closed by the ball valve 41 within the enlarge upper portion of the passageway. The ball valv is normally held to its seat closing the passage way by means of the coil spring 48 which i calibrated preferably to yield after the coil sprin 44 has yielded. The passageway 46 is in com munication at all times with the interior of th sleeve I4 of the lower piston body and, conse quently, with the upper cylinder 2 through th radial grooves 49 and 50, respectively, in th upper end of the cap 31 and the lower end of th valve body 40.

The parts are held in the normal or of! position by the coil spring 5I within the lower cylinde I and encircling the piston rod 5, the lower end o the coil spring abutting the ring 52, which in tur abuts the sealing cup 1. The upper end oi the coil spring abuts the cup-shaped retainer 53 which is sleeved on the piston rod5 and is held in engagement with the C-washer 54 engaging an annular groove in the piston rod. The upper end of the retainer clears the sealing cup I6 between its lips and is provided with milled radial grooves 55 to assure communication between the lower cylinder and the upper cylinder through the bypass means for the lower piston.

To prevent entrance of air into the lower cylinder I during the return stroke of the lower piston and other parts to their normal or oi positions, the plug 6 is formed with the concentric annular recess 56 at its upper end and inner edge and with the diagonal vair passageways 51 leading from the outer wall of the recess to the tool receiving sockets 58. The sealing cup 1 is preferably formed of rubber and has the concentric inner and outer upwardly extending lips 59 and 60, respectively, engaging the wall of the lower cylinder I and the piston rod 5. The sealing cup also has the concentric inner downwardly extending lip 6I located within the recess 56 and clearing its walls and engaging the piston rod 5. In the event that a vacuum is created in the lower cylinder I, air can enter the recess 56 to force the sealing lip 6I more firmly against the piston rod 5 to thereby secure a more effective seal. The plug 6 has an externally threaded portion of greater diameter than the internal diameter oi the lower cylinder I for threadedly engaging the lower end of the lower cylinder, and to prevent the leakage of air past the threads into the lower cylinder there is the gasket 62 which'is clamped between opposed shoulders on the plug and lower cylinder.

Referring to Figure 1 which sh'ows the parts in their normal or off positions, it will be noted that the lower cylinder I communicates with the upper cylinder 2 through the space above the retainer 53 and the radial grooves 55 in the retainer, the lower radial bores 30, the axial bore 32, the upper radial bores 3|, the interior of the sleeve I4, th'e transverse holes 26 in the sleeve, and the radial grooves 26 in the retainer 21. The reservoir 3 communicates with the interior of the sleeve I4 and, consequently, with the lower and upper cylinders I and 2 through the passageway 22, the annular enlargement 4I of the valve body 40 abutting the bottom wall of the cup 20, and the upper end of the side wall of the cup 2D abutting the depending annular ange of the upper end iitting 4. Also, the ball valve 41 is held to its seat closing the passageway 46 in the valve body 40. It will be noted that the coil springs 5I and 44 hold the parts, with the exception of the ball valve 41, in their normal or oil positions and that the coil spring 48 and gravity hold the ball valve in its normal or oil position closing the passageway 46.

When force is exerted pulling downwardly-on the piston rod to ,advance the pistons, the valve 39 is moved downwardly by means of the piston rod, the coil spring 44, the nut 45, and the shank 43 of the valve body to engage the lower face of the annular enlargement 4I of the valve body with the gasket 42 to close communication between the reservoir 3 and the interior of the sleeve I4 through the passageway 22. I'he clearance between the lower face of the annular enlargement and the gasket is less than the clearance between the lower face 34 of the piston rod enlargement 33 and the upper face 35 of the head I5 of the lower piston body so that after the enlargement has come into contact with the gasket the by-pass means for the lower piston I I is still open. During this initial downward movement of the piston rod, the coil spring 5I is slightly compressed. Figure 2 shows the positions of the parts at this time.

During the continued downward movement of the piston rod, the valve 40 moves the upper piston I2 downwardly, which in turn moves the lower piston II downwardly, the coil spring 5I being compressed independently of the pistons by reason of the retainer 53 and the C-washer 54. During this downward movement, braking uid flows from the upper cylinder to the lower cylinder through the by-pass means for the lower piston until the pressure of the braking fluid overcomes the coil spring 44. This pressure, as previously stated, is such that all clearance istaken up in the wheel brakes. Then upon compression of the coil spring 44 the lower face 34 of the annular enlargement 33 of the piston rod is seated against the upper face 35 of the head of the lower piston to close the by-pass means for the lower piston, after which and upon continued downward movement of the piston rod 5 the lower piston is moved directly by the piston rod and functions to force the braking fluid to the wheel cylinders. The pressure created by the upper piston I2 is relieved after the by-pass means for the lower piston is closed and during the continued downward movement of the piston rod by the braking lluid in th'e upper cylinder raising the ball valve 41 against the pressure exerted by the coil spring 48. At this time the partsare in the position shown in Figure 3.

Upon release of the pulling pressure upon the piston rod 5, the retracting coil spring 5I resiliently moves the piston rod, valve 39 and lower and upper pistons I I and I2, respectively, back to their normal or oil positions, during which time the coil springs 44 and 48 assume their normal positions. During the return stroke, it will be noted that braking fluid may pass from the reservoir 3 between the sleeve of the upper piston body and the wall of the upper cylinder and also between the outer lip of the sealing cup of the upper piston and the wall of the upper cylinder into the upper cylinder. Braking iiuid also may pass from the reservoir 3 through the axial passageway 22 into the interior of the sleeve I4 and through the by-pass means for the lower piston to the lower cylinder, or flow in the opposite dfrection. -v

In the modification illustrated in Figure 4, the fluid pressure control device has the same general arrangement of parts as that illustrated in Figures 1, 2 and 3, but differs in providing the -of the valve 10 and is provided with the head 'Il which is located between the lower end of the shank 69 and the base of the retainer 12. The

retainer extends within the chamber formed in the enlargement at the upper end of the piston rod and has an anular flange 'I3 at its upper end which is clamped between the cap 'I4 and the enlargement. The body of the valve III also differs from that of the previously described modiflcation in that it has xedly secured in its upper end the axial plug I5 which forms a -stop for the ball-valve 16. Furthermore, the body is provided with the diagonal passageways 'Il which open into the axial passageway in the body at the lower end of its enlarged portion'. The sealing cup 18 is provided within the chamber formed within the enlarged upper end portion of the piston rod below the retainer 'I2 to prevent braking y iluid from being forced from the lower cylinder into the upper cylinder through the portion of the piston rod slidably engaged by the plunger 83.

With this construction, after the piston rod has been lowered to an extent such that the lower face 66 of the annular enlargement 6l of the piston rod has engaged the upper face 68 of the body of the lower piston, the pressure created in the lower cylinder acts on the plunger 63 to raise the same which, in turn, raises the ball valve 16 from its seat so that the upper cylinder is placed in communication with the reservoir through the passageways, including the diagonal passageways TI. As a result, no appreciable effort is wasted in the displacement of the braking iluid by the upper piston.

It will be noted that the modification illustrated in Figure 5 differs from that of Figures 1, 2 and 3 in that the upper piston, the valve mechanism at the upper end of the piston rod,

and also the upper end portion of the piston rod, have been changed. The upper piston 'I9 has been changed essentially by providing the rub-v ber sealing cup with only an outer lip which is engageable with the wall of the upper cylinder 8I. The base of the sealing cup is clamped between the head 82 of the upper piston body and the enlargement 83 at the upper end of the sleeve 84 forming part of the body of the lower piston. Communication between the upper cylinder and the interior of the sleeve is provided by the diagonal passageways 85 in the enlargement 83.

The valve 86 for closing the axial passageway 81 in the upper piston body has its body 88 formed with the annular enlargement 89 for seating direct-ly upon the annular flange 90 of the upper piston body. The lower end of the valve body 88 also seats directly on the upper end of the cap 8|. In both instances lapped seats are formed to provide effective seals. The cap 9| forms a part of the piston rod assembly and is threaded upon the enlarged upper end of the piston rod 92 and forms therewith a chamber. A sealing ring 83 between the cap and the enlarged upper end of the piston rod prevents the flow of braking liquid past the threads and a lock nut 94 threaded on the enlarged upper end to lock the latter in place.

The valve body 89 is internally threaded for engagement with the axially extending hollow bolt 95 which extends axially downwardly through the cap 9| and has the head 96 within the chamber formed by the cap and piston rod. The bolt is preferably formed with the radial ports 91 below the valve body. 98 is a lock nut on the bolt abutting the upper end of the valve body.

99 are rmless frusto-conical snap springs arranged in series between the bolt head 99 and the cap 9| for resiliently holding the valve 8B seated on the cap 9|. The snap springs are so constructed that they provide for snap or sudden movement of the piston rod 92 relative to the valve 86 a distance equalto the clearance between the lower face of the annular enlargement |0| of the piston rod and the central upper raised face |02 of the lower piston body when the predetermined pressure of braking iluid in the cylinders has been reached. In the normal or oi positions of the parts, the snap springs hold the valve 88 in contact with the cap 9| but when the predetermined pressure has been created in the cylinders snap movement of the piston rod relative to the valve takes place to instantly seat the enlargement |0| of the piston rod upon the lower piston body to close the bypass means for the lower piston. At the same time the relief passageway, including the radial ports 91 and the axial passageway through the hollowbolt, isopened providing communication between the upper cylinder and the reservoir. With this arrangement, either the by-pass means for the lower pistonor the relief passageway for the upper cylinder can be open depending upon the fluid pressure, but neither can be partly open at the same time.

The snap springs 99 are preferably provided with the holes |03 which permit free passage of the braking iluid through the snap springs so that the braking fluid may lubricate the snap springs and their contacts with the cap and hollow bolt. The holes may be of such size that, if desired, the radial ports 91 may be eliminated.

With this arrangement, the snap springs are preloaded to any desired value by adjusting the hollow bolt 95 relative to the valve 86, the upper end of the bolt being slotted for this purpose. The bolt may then be locked in adjusted position by the lock nut 98. The amount of travel during the snap action of the snap springs is controlled by turning the cap 9| relative -to the piston rod 92 and then locking by means of the nut 94. This latter adjustment controls the Width of the passage between the faces |00 and |02 of the piston rod and lower piston body, respectively, after the valve body 88 has seated on the annular flange 90 of theupper piston body, the width of the passage corresponding to the amount the snap springs can snap.

In the modification illustrated in Figure 6. the frusto-conical snap springs |04 are arranged in parallel between the bolt head |05 and the top of the cap |06 with the annular spacers |01 and |08 between the snap springs, respectively at their inner and outer edges. The snap springs are preferably formed with the holes |09 therethrough for the purpose of reducing friction when the springs are in operation. These holes will also permit eliminating the transverse ports in the bolt.

Figure '1 shows another modification in which of the piston rod abuts the lower end of the cap the frusta-conical snap springs III are arranged in parallel and touching each other. These snap springs are also preferably provided with the holes I therethrough which permit the braking iluid to enter between the snap spring due to capillary action and provide` sufficient lubrication so that the friction between the springs will not be objectionable. If desired, the radial ports in the hollow bolt may be eliminated. in which case the braking fluid after passing between the valve body and the tcp of the cap passes downwardly through the holes l| to the axial passageway in the bolt.

In the modification illustrated in Figure 8. the frusto-conical snap springs ||2 are arranged in parallel and they are'provided with rolled inner and outer .rims ||3 and Ill, respectively. The rolled rims serve to control the deilectional characteristics of the snap springs and to space the same to thereby avoid the necessity of spacers, such as shown in Figure 6. v

Figure 9 discloses another modirication in which the frusto-conlcal snap springs Il 5 are ar ranged in series and formed with rolled inner and outer rims.

It will be noted that the snap springs of both Figures 8 and 9 are preferably formed with holes therethrough so that both modifications may operate in the same manner as those previously described.

What I claim as my invention is:

1. A uid pressure contrcldevice comprising a cylinder having a discharge port, asecond cylinder of larger diameter than said first mentioned cylinder, a piston slidable within said first mentioned cylinder, a second piston slidable within said second cylinder and positively connected to said first mentioned piston, a fluid reservoir, said second piston having a passageway therethrouh for placing said second cylinder and reservoir in communication, avalve movable axially relative to said second piston for closing said passageway and moving said second piston, said valve having a passageway therethrough for placing said second cylinder in communication with said reservoir, means carried by said valve for normally closing said second mentioned passageway, a piston rod movable axially relative to said ilrst mentioned piston and having a passageway for placing said cylinders in communication, and a yieldable connection between said valve and piston rod for moving the former through the latter, said connection being yieldable when a predeter mined pressure within said iirst mentioned cylinder has been created whereby said piston rod moves relative to said first mentioned piston to close the passageway in said piston rod and said means carried by said valve opens to place said second cylinder in communication with said reservoir.

2. A fluid pressure control device comprising a pair of cylinders of different diameter, the smaller diameter cylinder having a discharge port, pistons slidable in unison in said cylinders, means for placing said cylinders in communication, a iluid reservoir, means for placing the larger diameter cylinder in communication with said reservoir, means for moving said pistons forward comprising a valve for closing said last mentioned communication means, a rod, and a connection between said valve and rod yieldable when a predetermined pressure within one of said cylinders is created, means on said rod for closing said rst mentioned communication means upon yielding of said connection, and other means for placing the larger diameter cylinder in communication with said reservoir when a predetermined pressure within one of said cylinders is created to relieve the fluid pressure in the larger diameter cylinder.

3. A iiuid pressurecontrol device comprising axially aligned lower and upper cylinders, said upper cylinder being of larger diameter than said lower cylinder, a fluid reservoir above said upper cylinder, lower and upper pistons within said cylinders movable in unison, by-pass means for said lower piston to place said lower and upper cylinders in communication, said upper piston having a passageway therethrough for placing said upper cylinder in communication with-said reservoir, a valve movable forwardly to close said passageway and then move said upper piston forwardly, a piston rod, a yieldable connection be- 'means upon yielding of said connection, and

means for placing said upper cylinder in communication with said reservoir upon yielding of said connection. 4

4. A uid pressure control device comprising a cylinder having a discharge port, a second cylinder of larger diameter than said first mentioned cylinder, a piston slidable within said rst mentioned cylinder, a second piston slidable within said second cylinder and positively connected to said first mentioned piston, a iiuid reservoir, said second piston having a passageway therethrough for placing said second cylinder and reservoir in communication-a valve movable axially relative to said second piston for closing said passageway and then moving said second piston, said valve having a passageway therethrough for placing said second cylinder in communication with said reservoir, a second valve for normally closing said second mentioned passageway, a piston rod movable axially relative to sai d iirst mentioned piston and having a passageway for placing said cylinders in communication, a yieldable connection between said first mentioned valve and piston rod for moving the former through the latter, said connection being yieldable when a predetermined pressure, within said first mentioned cylinder has been created whereby said piston rod moves relative to said rst mentioned piston to close the passageway in said piston rod, and yieldable means for holding said second valve closed, said last mentioned means being yieldable tween said valve and piston rod for moving the when a predetermined pressure has been created in said second cylinder whereby said second valve moves to open position 5. A fluid pressure control device comprising a pair of cylinders of dierent diameter, the smaller diameter cylinder having a discharge port, pistons slidable in unison in said cylinders, means ior placing said cylinders in communication, a iiuid reservoir, means for placing the larger diameter cylinder in communication with said reservoir, means for moving said pistons forward comprising a member for closing said last mentioned communication means, a second member for closing said first mentioned communication means and a yieldable member connecting said iirst mentioned member and said second member, said member being yieldable when a predetermined pressure within one of said cylinders is created. and other means for placing the larger diameter cylinder in communication with said reservoir when a predetermined pressure within one oi said cylinders is created.

6. A fluid pressure 'control device comprising axially aligned lower and upper cylinders, said upper cylinder being of larger diameter than said lower cylinder, a fluid reservoir above said upper cylinder, lower and upper pistons within said cylinders movable in unison, by-pass means for said lower cylinder to place said lower and upper cylinders in communication, said upper piston having a passageway therethrough for placing said upper cylinder in communication with said reservoir, a piston rod provided with means for closing said by-pass means and moving said lower piston, a valve for closing said passageway through said upper piston and moving said upper piston forwardly, said valve having a longitudinal passageway therethrough opening into said reservoir and also having a por tion engageable with said piston rod to close said last mentioned passageway, and a yieldable connection between said piston rod and valve for moving the latter forwardly, said connection being yieldable when a predetermined pressure within said lower cylinder is created to provide for movement ci' said piston rod relative to said valve. v

7. A iiuid pressure control device comprising a cylinder having a discharge port, a second cylinder of larger diameter than said first mentioned cylinder, a piston slidable within said iirst mentioned cylinder, a second piston slidable within said second cylinder and positively connected to said first mentioned piston, a uid reservoir, said second piston having a passageway therethrough for placing said second cylinder and reservoir in communication, a valve movable axially relative to said second piston for closing said passageway and then moving said second piston, said valve having a passageway therethrough for placing said second cylinder incommunication with said reservoir, a second valve for normally closing said second mentioned passageway, a piston. rod movable axially relative to said first mentioned piston and having a passageway for placing said cylinders in communication and a portion engageable with said first mentioned piston to close said last mentioned passageway and positively move said rst mentioned piston, a yieldable connection between said iirst mentioned valve and piston rod for moving the former through the latter, said connection being yieldable when a predetermined pressure within said iirst mentioned cylinder has been created wherevby said piston rod moves relative to said rst mentioned piston, and a plunger within said piston rod engageable with said second mentioned valve to move the same to open position, said plunger being movable after said connection has yielded under the iiuid pressure created in said first mentioned cylinder.

8. A fluid pressure control device comprising a pair of cylinders of different diameter, the smaller diameter cylinder having a discharge port, pistons slidable in unison in said cylinders. means for placing said cylinders in communication, a fluid reservoir, means for placing the larger diameter cylinder in communication with said reservoir, means for moving said pistons forward comprising a piston rod provided with means for closing said rst mentioned'communication means, a valve for closing said last mentioned communication means, said valve normally seating on said piston rod, arbolt extending voir, and means for advancing said pistons comprising a piston rod, a valve for closing said passageway, a hollow bolt having a longitudinal passageway communicating with said reservoir, said bolt being mounted on said valve, and frustoconical snap spring means operatively connected to said piston rod and bolt for resiliently holding said valve seated on said piston rod to close communication between one of said cylinders and 10 the interior of said bolt.

LUDWIG A. MAJNERI. 

